Tuning of Fermi level position at HfNx/SiO2 interface

We demonstrate that the vacuum work function of HfNx, as measured in situ by Kelvin probe, can be tailored on the entire silicon band gap by changing the nitrogen content of the HfNx alloy. We observed an increase in the effective work function of HfNx on SiO2, extracted from capacitance-voltage measurements, only for x<1, and saturation is reached at a value of 4.6 eV for x>1. The measured value of the effective work function for pure Hf (4.1 eV) can be explained by the metal induced gap states model, while the HfNx behavior is explained by oxidation at the HfNx/SiO2 interface.